Halogenated phenylmalonates are useful as intermediates for the preparation of a variety of compounds which are useful as agrochemicals, pharmaceuticals or liquid crystals. In particular, they are key intermediates in the preparation of fungicidal 6-(halophenyl)-triazolopyrimidines which are described for example in EP 0 550 113 and WO 94/20501.
J. Setsune et al., Chemistry Letters, pp. 367-370, 1981 disclose a method of coupling phenylhalides with sodium diethylmalonate in the presence of copper(l) salts. However, good yields are obtainable only with phenylbromides substituted with electron withdrawing groups when 1 equivalent of phenylbromide is reacted with 1.2 equivalents of sodium diethylmalonate according to this document. Moreover, use of two equivalents of sodium diethylmalonate gave even lower yields.
The use of 5 equivalents of sodium diethylmalolanate as suggested by R. Ugo et al., Gazzefta Chimica Italiana, 122,1992, pp. 511-514, is not possible with arylbromides substituted by two or more halogen atoms, since undesired side-reactions will occur and decrease the yields.
Therefore, the methods known from the prior art are not entirely satisfactory for large scale production, since the yields of the reactions starting from halogenated phenylbromides are often low.